1. Field of the Invention
The present invention relates to a prefabricated element for use in a system of sound insulation and absorption for dwellings. More particularly, this invention relates to a prefabricated element placed on a single wall of a room to form a double sound insulation and absorption wall, comprising a frame which supports a flexible panel by means of an elastic sealing means to thereby position the flexible panel at a predetermined distance from the wall.
2. Description of the Prior Art
It is known that certain existing dwellings are insufficiently protected against external sounds coming partly from other rooms situated in the same building and partly from external sounds such as road and railway traffic noise. To improve the sound insulation of a dwelling, prefabricated elements have been placed on at least one of the walls of the dwelling, and notably on the floor and/or under the celling, so that the double wall thus formed allows the sound attenuation coefficient of the single wall to be increased and the elements placed on the wall act as a partial sound absorber, mainly at frequencies less than 300 Hertz.
A prefabricated element of this type comprises a flexible panel of compact material supported parallel to the single wall at a distance d from the latter by parallelepipedal cross members of a frame connected preferably by means of elastic material to the single wall in order to suitably decouple the single wall and the prefabricated element. When the double wall is acted on by sound waves, the flexible panel vibrates at a resonance frequency f which expresed in Hertz is given by the relation (Book entitled "Notions d'acoustiques" by Robert Josse, Editions Eyrolles, 1973, page 157). EQU f=60/.sqroot.md (1)
where m is equal to the surface mass (mass per area unit of surface) expressed in kg/m.sup.2 of a flexible panel which is assumed, according to usual practice, to be very much smaller than that of the single wall and d is the width of the air layer of the double wall expressed in meters. In this case, the sound attenuation coefficient of the double wall increases as a function of the frequency more rapidly than that of the single wall above the frequency f. It is thus preferable to choose a product md as large as possible. This product md is determined by reconciling the size boundaries of the prefabricated element contributing to the reduction in volume of the room and the loading boundaries of the walls dependent on the structure of the room and the requirement to obtain sufficient insulation of the room. Furthermore, since these prefabricated elements are built with standardized dimensions in order to reduce the cost of manufacture, the frequency f is chosen such that it is sufficiently low to allow efficient insulation of existing dwellings, and such that at the same time it corresponds to an annoying frequency determined qualitatively by measurement inside the dwellings.